1. Field of the invention
The present invention relates to a method or and a device for measuring the densities of different kinds of photo-sensitive toners constituting a photo-sensitive toner mixture which is used to form a color image by a single exposure and developing operation, and more particularly to a method of and a device for measuring the densities of three kinds of photo-sensitive toners constituting a photo-sensitive toner mixture, the photo-sensitive toners being colored cyan, magenta, and yellow, respectively, and becoming conductive by being exposed to three kinds of light, respectively, each light having wavelengths in a color region complementary to the color of each toner.
2. Description of the prior art
In recent years, a method of forming a color image by a single exposure and developing operation using photo-sensitive toners has been attracting attention. This kind of color image forming method uses three kinds of photo-sensitive toners colored cyan, magenta, and yellow, respectively. The photo-sensitive toners are sensitive to the light of colors complementary to the respective toner colors, i.e., the cyan toner is sensitive to red light, the magenta toner to green light, and the yellow toner to blue light, each becoming conductive by being exposed to its complementary light. When electrically charged photo-sensitive toners are exposed to the respective kinds of light to which they are sensitive, they become conductive and lose their electrical charge (hereinafter referred to as "discharged").
The following describes an example of the above color image forming method using photo-sensitive toners of different colors. First, a mixture of the above three kinds of photo-sensitive toners is uniformly charged, and then, light that contains information of a color image is projected onto the photoconductive toner mixture. For example, green light is projected to the areas on the photo-sensitive toner mixture that correspond to the green parts of the image to be formed, so that, in those areas, magenta toner sensitive to green light becomes conductive and is electrically discharged, while the yellow and cyan toners do not become conductive but remain charged. Likewise, the areas corresponding to the blue parts of the image are exposed to blue light, so that the yellow toner in those areas is discharged, while the cyan and magenta toners remain charged; with red light projected to the areas corresponding to red parts of the image, the cyan toner in those areas is discharged, but the magenta and yellow toners remain charged. Thereafter, the thus discharged photo-sensitive toners are separated from the charged photo-sensitive toners, and then the charged photo-sensitive toners are transferred onto copy paper to form a final color image thereon.
In the above method of forming a color image, however, all kinds of photo-sensitive toners are not equally consumed, but the consumption amount differs among the toners according to the color tone of the image to be formed. Therefore, as the image forming operation is repeated, the unevenness in the consumption of the photo-sensitive toners becomes greater, and there may arise, for example, a possibility of the ratio of one kind of toner to the whole photo-sensitive toner mixture (the toner density in the photoconductor toner mixture) decreasing. If the density of one kind of photo-sensitive toner decreases, the color produced with that photo-sensitive toner will not come out clear, thus impairing the quality of the final image produced.
Japanese Laid-Open Patent Publication No. 62-209560 discloses a method of measuring transferred amounts of different kinds of color toners. However, this method is not used for measuring different kinds of color toners constituting a color toner mixture, but it is only applicable to a color image forming method in which an exposure process and a developing process are performed for each kind of color toner and the resultant toner images are superimposed on each other to produce a final color image. Therefore, it is not applicable to the aforementioned method of forming a color image by a single exposure and developing operation using a mixture of different kinds of photo-sensitive toners.